test(core): add regression tests for incorrect pagination cursor extraction

[niklashigi]

This prepares the fix for #12 - the resolution itself is made using a change to our SDK-specific OpenAPI (not tracked in this repo)

---

Note

Add comprehensive pagination tests and make mock request body parsing more robust in test utilities.

• Tests:
  • Add pagination behavior tests in tests/test_pagination.py covering:
    • Iteration across multiple pages and request count validation
    • Passing cursor to subsequent requests
    • Stopping when next is null
    • Preserving original query params across pages
    • Manual pagination via next()
• Test Utilities:
  • In tests/conftest.py, enhance MockContext request capture to parse non-GET request bodies by trying JSON first and falling back to raw string on decode/parse errors.

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[cursor]

Bug: Exception handler will re-raise same UnicodeDecodeError

The exception handler catches UnicodeDecodeError from the decode() call on line 95, but then the fallback on line 98 calls request.content.decode() again. If the original error was a UnicodeDecodeError, this second decode call will raise the same exception, which won't be caught. The fallback needs to handle the case where the content cannot be decoded as UTF-8, such as by specifying an error handler (e.g., decode(errors='replace')) or storing raw bytes.